docs: def prune(self):
          """
          Do an exclude for all Users who have a SentDrip already.
          """
          target_user_ids = self.get_queryset().values_list('id', flat=True)
          exclude_user_ids = SentDrip.objects.filter(date__lt=conditional_now(),
                                                     drip=self.drip_model,
                                                     user__id__in=target_user_ids)\
                                             .values_list('user_id', flat=True)
          self._queryset = self.get_queryset().exclude(id__in=exclude_user_ids)